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Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation

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Abstract

This study contributes to the knowledge about the capabilities of the popular “six-directional method” describing the radiation fields outdoors. In Taiwan, measurements were carried out with three orthogonally placed net radiometers to determine the mean radiant temperature (T mrt). The short- and long-wave radiation flux densities from the six perpendicular directions were recorded in the daylight hours of 12 days. During unobstructed direct irradiation, a specific daytime relapse was found in the temporal course of the T mrt values referring to the reference shapes of a standing man and also of a sphere. This relapse can be related to the short-wave fluxes reaching the body from the lateral directions. Through deeper analysis, an instrumental shortcoming of the six-directional technique was discovered. The pyranometer pairs of the same net radiometer have a 10–15-min long “blind spot” when the sun beams are nearly perpendicular to them. The blind-spot period is supposed to be shorter with steeper solar azimuth curve on the daylight period. This means that the locations with lower geographical latitude, and the summertime measurements, are affected less by this instrumental problem. A methodological shortcoming of the six-directional technique was also demonstrated. Namely, the sum of the short-wave flux densities from the lateral directions is sensitive to the orientation of the radiometers, and therefore by deviating from the original directions, the T mrt decrease on clear sunny days will occur in different times and will be different in extent.

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Acknowledgments

The authors would express a special thank for the sponsorship of the Research Center for the Humanities and Social Sciences at the National Chung Hsing University.

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Authors and Affiliations

  1. Program of Landscape and Recreation, Research Center for the Humanities and Social Sciences, National Chung Hsing University, 250 Guoguang Road, South Dist, Taichung City, 40227, Taiwan, Republic of China

    Noémi Kántor

  2. Department of Architecture, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan, Republic of China

    Tzu-Ping Lin

  3. Chair of Meteorology and Climatology, Alberts-Ludwigs-University Freiburg, Hebel Str. 27, D-79104, Freiburg, Germany

    Andreas Matzarakis

Authors
  1. Noémi Kántor
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  2. Tzu-Ping Lin
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  3. Andreas Matzarakis
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Correspondence to Noémi Kántor.

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Appendix 1

(a) series: Sun-path properties and the corresponding radiation conditions in Huwei on the four cardinal days of the year: (a.1) Spring Equinox, (a.2) Summer Solstice, (a.3) Autumn Equinox, (a.4) Winter Solstice; (b–d) series: absorbed short-wave flux densities on the same days from the two vertical (K *vert ), from the four lateral (K *lat ), and from all the six perpendicular directions (K*) in the cases of spherical (sp.) and standing (st.) reference shapes, and with different orientations: (b) series: N–E–W–S (0° deviation), (c) series: NNE–ESE–SSW–WNW (22.5° deviation), (d) series: NE–SE–SW–NW (45° deviation) (JPEG 1327 kb)

Appendix 2

(a) series: Sun-path properties and the corresponding radiation conditions in Göteborg on the four cardinal days of the year: (a.1) Spring Equinox, (a.2) Summer Solstice, (a.3) Autumn Equinox, (a.4) Winter Solstice; (b–d) series: absorbed short-wave flux densities on the same days from the two vertical (K *vert ), from the four lateral (K *lat ), and from all the six perpendicular directions (K*) in the cases of spherical (sp.) and standing (st.) reference shapes, and with different orientations: (b) series: N–E–W–S (0° deviation); (c) series: NNE–ESE–SSW–WNW (22.5° deviation); (d) series: NE–SE–SW–NW (45° deviation) (JPEG 1469 kb)

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Kántor, N., Lin, TP. & Matzarakis, A. Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation. Int J Biometeorol 58, 1615–1625 (2014). https://doi.org/10.1007/s00484-013-0765-5

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  • DOI: https://doi.org/10.1007/s00484-013-0765-5

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